The magnetic compass has been a standard accessory on various vehicles ever since its introduction. Although not as necessary a navigational instrument as it is in a boat or an airplane, the compass is a very useful instrument for an automobile when traveling in an unfamiliar territory. However, since the compass is not so vital an instrument in an automobile, little attention was previously given to improving its readability.
In the traditional magnetic compass, a magnetic bar was attached to a display disk having a center pivot. The disk and magnet were suspended in a damping fluid to reduce oscillations of the display while turning or encountering external vibrations. The method of marking the disk for indicating the direction greatly affected the manner in which directional information was conveyed to the user. Several types of displays have heretofore been utilized. In one arrangement, the disk is flat and marked in the usual North, South, East and West orientations. The direction is indicated by a fixed reference line (lubber line) at the top of the disk. Since the disk is horizontal, the display must be viewed from the top. This arrangement will give an overall view of the direction the vehicle is traveling and where the desired directions are relative to the current heading. This type of compass display is usually found on large boats where space is not a premium and the compass can be placed so that the operator can easily view the compass disk from above.
In an airplane or automobile, where it is not practical to place the compass in a location where it can be viewed from the top, the display must be arranged differently. For example, the compass disk may be a cylinder or half sphere with the legends printed around the edge. Here the direction is indicated by the lubber line which is placed between the cylinder and the observer. The compass legends are rotated 180.degree. to compensate for the position of the lubber line and as a consequence, the relative compass directions are read backwards. For example, if the vehicle is traveling North and the desired direction to travel is North-East, the vehicle must turn to the right 45.degree. but the North-East direction is shown as being 45.degree. to the left of the current direction. Users must adapt to this reversal of directions even though it is not intuitively obvious to the untrained user how to interpret the appropriate direction. In addition, only about one-third of the compass directions are visible at any one time since one cannot see all the way around the cylinder.
Where it is important to view all of the directions simultaneously and to eliminate any directional ambiguity problems as in an airplane, the standard magnetic compass is supplemented with a vertical card directional gyro. The display for the directional gyro is similar to the marine compass described earlier, and the lubber line may be replaced with an airplane symbol. Using the previous example, if the aircraft is traveling north and wishes to turn North-East, both the actual direction and the turn are shown to be 45.degree. to the right. In fact at any time, the directional gyro gives a view of all the compass directions and the relative orientation of the aircraft as it would be seen by an observer from above.
A fourth type of compass display is usually found only on a flux gate or gyro compass on large aircraft and is used as a reference instrument only. It consists of a fixed card which is marked in the normal North, South, East and West orientations and the direction is indicated by a moving pointer which rotates around the disk. Although this display give reasonably comprehensible displays for Northerly headings, the display is reversed for Southerly headings. For example, if the vehicle is traveling South-East and wishes to travel South, the vehicle must turn right, but South is indicated to be to the left of the pointer. One advantage of this type of display is that all of the direction legends are printed right side up and as such are more easily read than the previous display examples.
Having established the shortcomings and limitations of the aforesaid devices, it became apparent that a new and different approach was required in order to provide an improved electronic compass detector with an electronic display system particularly adaptable for automobiles. For such an electronic compass, a particular problem arose of providing a display which would provide the same spatial orientation and functional advantages as the directional gyro display used in modern aircraft. However, in an electronic compass display (i.e., an LED, LCD or vacuum fluorescent display) the presentation is normally not continuous as it is in the mechanical display. Therefore, it must be broken down into discrete segments which can be individually energized by the driving electronics. The choice as to how many segments to divide the compass display into determines the complexity of the display and the driving electronics. Usually the compass is divided into 16 segments yielding a resolution of 22.5.degree. per segment.
To construct an electronic analog of the vertical card compass with 22.5 degree resolution, would require that there be one each of the North, South, East and West legends in each of the 16 locations. This would require 64 driving elements in addition to what would be required to illuminate any reference marks around the display. In addition to the large number of driving elements required, an additional problem with such a display is that the associated legends would have to be so small that they would become unreadable at a distance.
Because of the complexity of duplicating all of the direction labels in all the possible locations for a rotating card type compass display, prior electronic displays appeared as a fixed card with a moving reference, similar to the gyro compass display. Here, the legends can be quite large and readable and the drive requirements for such displays are quite simple, requiring only as many driver outputs as divisions in the compass display (typically 16). However, this prior display retained the problem of directional ambiguity especially for Southern headings.
It is therefore an object of this invention to provide an all electronic compass and a display therefor with an analog of a moving card, fixed reference compass display which gives unambiguous directional information but with the driving simplicity of a fixed card, moving reference display.
Another object of this invention is to provide an electronic compass with a display having an analog of a moving card compass display with large enough legends to allow it to be read from a reasonable distance.
It is a further object of this invention to provide a moving card compass display which keeps all of the direction legends in an upright legible orientation at each location around the compass rose.
It is a further object of this invention to provide a display for an electronic compass which gives a perspective view of the road ahead and the compass directions as they would be seen by the driver of the vehicle in such a way as to provide a display which is intuitively visually realistic and thus readable even to the untrained user.
Another object of the invention is to provide an electronic compass which is accurate, reliable, compact, easy to install and yet highly readable in use.